The present invention relates to novel, recombinant deoxyribonucleic acids (DNA), to vectors and host organisms which contain them, and to transgenic plants which contain the recombinant DNA and exhibit increased resistance toward pernicious organisms and plant diseases.
For a number of viruses, it has already been shown that when either structural or non-structural genes are isolated from these viruses and induced, in a suitable manner, to express in transgenic plants, they give rise, in the plants, to increased resistance toward infection by the homologous virus or to attenuation and/or slowing down of symptom manifestation. This was demonstrated for the first time using the example of the coat protein of tobacco mosaic virus (TMV) (EP-A2-0 223 452; Beachy et al., 1985; and Powell Abel et al., 1986). TMV belongs to the Tobamovirus genus and has a comparatively simple architecture and, for its genetic information, possesses, like many other plant viruses, a single-stranded RNA molecule having plus-strand information (single-stranded positive-sense RNA genome). The genetic information is packaged in a coat which consists of many identical subunits. Later on, it was possible to show that a comparable strategy also succeeded in the case of the tomato spotted wilt virus (TSWV), which is a virus which is essentially different and belongs to the Tospovirus genus of the Bunyaviridae family (EP-A1-0 426 195; Gieien et al., 1991; De Haan et al., 1992). The genus Tospovirus is classified as having a morphologically spherical particle of about 100 nm in diameter and a three-partite, single-stranded RNA genome, which, as a nucleoprotein complex (nucleocapsid), is surrounded by a lipid coat. This lipid coat is charged with glycoproteins.
The three-partite genome possesses ambisense or minus-strand information (single-stranded RNA molecules of negative or ambisense polarity, De Haan et al., 1990). In this case, resistance in transgenic plants is based on transferring the N structural gene of a tospovirus, the tomato spotted wilt virus (=TSWV) into a plant, where it is expressed. The N gene product is a component of the abovementioned nucleoprotein complex.
Whereas it was possible to demonstrate pronounced cross resistance toward closely related tobamoviruses in the case of the TMV coat protein (e.g. Tumer et al., 1987), such cross resistance is not so far known in the case of TSWV and expression of the N gene (De Haan et al., 1992; MacKenzie and Ellis, 1992; Sheng-Zi et al., 1992).